The present invention is directed to an improved screen holder mechanism for rotary screens in a rotary screen printing machine.
Many types of screen holder mechanisms are known. The function of such mechanisms is to not only axially and radially or guide a rotary screen in a desired printing position in a rotary screen printing machine, but also to axially tension the rotary screen. Such screen holder mechanisms are usually provided with mounting arrangements which are adjustable so that they may be used for supporting screens of various different diameters. The screen holder mechanisms support the rotary screens in the printing machine in a position whereat the screens may be rotated. The screen holder mechanisms, due to the fact that the rotary screens are very thin walled, are movable in a direction axially of the screen, and thereby impart axial tension to the screen. Such mechanisms normally include two screen holders, one at each end of the screen. One or both of these screen holders are movable to provide the axial tensioning of the screen.
Among the various known screen holder mechanisms, most of them are extremely complicated and result in the necessity for considerable amounts of work to mount a screen in or remove a screen from the mechanism.
To overcome this disadvantage, it has become known to provide a screen holder mechanism which is completely accessible from above, i.e. such that the rotary screen may be easily mounted in or removed from the mechanism at any angular position of the screen.
One such arrangement is shown in U.S. Pat. No. 3,565,002 wherein the screen holder mechanism is completely accessible from above and wherein the rotary screen may be readily mounted in or removed from the mechanism. However, this mechanism has the disadvantage that during operation the rotary screen has an uncontrolled tendency to lift upwardly, thereby seriously affecting the quality of printing. This is due to the fact that the weight of the screen is normally insufficient to insure its continuous operative position, and the screen therefore tends to lift upwardly.
A further known screen holder mechanism which is completely accessible from above overcomes this disadvantage. Specifically, the mechanism described in U.S. Pat. No. 3,565,001 discloses a screen holder mechanism which is completely open from above and wherein the screen is prevented from uncontrolled lifting by a plurality of annular recesses and bosses arranged around each end of the screen. However, this arrangement, although preventing uncontrolled lifting of the screen, has the further very distinct disadvantage.